They like the idea of hanging with the "bad boys", because it's exciting and they're bored.
Like American girls who like having "gangsta" thugs as boyfriends.
These girls have a fair chance of being the modern incarnation of the teenaged girls who became sadistic female guards in the Nazi concentration camps.
There are evil women who would like to join the ISIS female brigade that threw acid in 15 women’s faces for refusing to wear a niqab and likes to shoot people.
Then they may just be stupid, hoping to marry a man and become the first wife of a new caliph.